Some thermal printers print images by thermally transferring the inks of an ink ribbon onto a printing medium, such as a paper roll, with a thermal head. In such a thermal printer, the paper roll, when used as a printing medium, has an unlimited length in its transfer direction (also referred to as the “vertical scanning direction”). On the other hand, the ink ribbon contains, for instance, a yellow (Y) ink, a magenta (M) ink, a cyan (C) ink, and an OP (i.e., coating) ink each having a specified size. The ink sizes thus limit a printing size. Accordingly, the ink ribbon needs to be changed in conformance with a desired printing size.
Printing an image that is long in the vertical scanning direction, such as a panoramic image, requires an ink ribbon in conformance with a long printing size. Such ink ribbons are unfortunately less available and thus expensive.
To address this problem, panorama printing is provided that is a means for printing an image longer than an ink ribbon of specified printing size, such as a panoramic image. In the panorama printing, the panoramic image is divided to be printed in combination with the ink ribbon of specified printing size. Dividing the panoramic image into a plurality of images as small as or smaller than the printing size of the ink ribbon enables printing with the ink ribbon of specified printing size. Further, printing the panoramic image multiple times so as to join the divided images together provides a single printed image. In the printing by joining the divided images together, printing with the images partly overlapping each other without any processing produces a conspicuous seam. This unfortunately degrades the quality of the printed image.
To address this problem, Patent Document 1, for instance, describes reducing the difference in concentration between the images at the seam, thus improving the image quality. Moreover, Patent Document 2 describes improving the image quality by individually changing, at the seam, the correction of a portion to be printed first and the correction of a portion to be printed later so that the concentration of the portion at the seam is uniform.